WHEN it comes to conjuring up the most mean-spirited insults a mother could hurl at her son, leave it to Ryan Gosling.

In his latest film, Only God Forgives, the Canadian actor plays a drug-smuggling mama's boy. In one scene, his character is humiliated by his mother at dinner after he brings a hooker, posing as his girlfriend, to meet mom - played by Kristin Scott Thomas.

Gosling said the embarrassments heaped on his character - including comments about his anatomical shortcomings - weren't originally in the script.

"She had to emasculate me and so she asked me to help, which I thought was funny. We just worked together and I told her all the things that she could say to me that would be sort of castrating," Gosling said, smiling. "She has that whole crazy rant."

Scott Thomas said while it was fun to play the villainous character, the darkness in her soul was "debilitating and wears you down."

And then there's the dinner scene.

"All I can remember was there was these huge pages and pages of words, and some of them were very, very difficult to say," Scott Thomas said. "He (Gosling) came up with that dialogue, believe me."

Scott Thomas said hurling insults as Gosling's ice queen mum in the film was "very, very difficult". Picture: AP

Scott Thomas said it takes a certain type of actor to be able to handle some of the more sensitive comments hurled at his character.

"You can rely on him. He's not going to flake. He's not going to suddenly stop being in the scene. He's not going to judge you by the way you're interpreting something," Scott Thomas said of Gosling, adding: "To have somebody that I could completely rely on to be there and not kind of laugh ... was sort of helpful."

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